1. BioCentrum Amsterdam, University of Amsterdam, Department of Molecular Cytology, Kruislaan 316, 1098 SM Amsterdam, The Netherlands,
2. Center for Ultrafast Optical Science, University of Michigan, 2200 Bonisteel Blvd, IST Building, Ann Arbor, MI 48109–2099, U.S.A.,
3. Department of Electrical and Computer Engineering, University of California, San Diego, Urey Hall, Mail Code 0339, La Jolla, CA 92093–0339, U.S.A.